Fm. Menger et al., SYNTHESIS AND THERMOTROPIC PROPERTIES OF MACROCYCLIC LIPIDS RELATED TO ARCHAEBACTERIAL MEMBRANES, Journal of the American Chemical Society, 115(15), 1993, pp. 6600-6608
Macrocyclic phospholipids containing 32-44 ring atoms were synthesized
by a route involving a high-temperature Glaser oxidation as the key s
tep. These lipids are analogous to mammalian phospholipids except a si
ngle extra carbon-carbon bond joins the chain termini. The new lipids
offered, therefore, an opportunity to examine thermotropic properties
of their membranes when the chains within a given molecule are unable
to move independently of one another. It was concluded that chain ''te
thering'' (a) raises the transition temperatures substantially for all
but the shortest lipids, (b) lowers enthalpies of transition by, in p
art, reducing the number of gauche C-C linkages created during the mel
ting process, and (c) lowers entropies of transition by impeding motio
nal freedom with in the liquid-crystalline phase. Molecular mechanics
calculations on the macrocyclic lipids are described briefly.